Products
Dopamine agonists are commercially available in the form of tablets, sustained-release tablets, transdermal patches, and injectables, among others.
Structure and properties
The first active ingredients, such as bromocriptine (Figure), were derived from ergot alkaloids. These are referred to as ergoline dopamine agonists. Later, agents with a nonergoline structure, such as pramipexole, were also developed. Because of their different structure, the dopamine agonists do not undergo the same metabolism as dopamine and can be administered at a lower dose. Combination with a decarboxylase inhibitor is not required.
Effects
Dopamine agonists have dopaminergic properties and inhibit secretion of the anterior pituitary hormone prolactin. The effects are due to agonism at dopamine receptors. The agents differed in their selectivity for receptor subtypes.
Indications
Indications for use include:
- Parkinson’s disease, as monotherapy or in combination with levodopa.
- Idiopathic restless legs syndrome.
- Prolactinomas
- Lactation inhibition (weaning)
Other indications:
- As emetic
- Erectile dysfunction
- Acromegaly
- Prolactin-related hypogonadism in men
- Menstrual cycle disorders and infertility in women
- Amenorrhea
- Oligomenorrhea
- Drug-induced hyperprolactinemic disorders.
- Polycystic ovary syndrome
- Anovulatory cycles
Dosage
According to the professional information. Dosage depends on the drug and the indication, among other factors. Dopamine agonists are administered perorally, transdermally, sublingually, and parenterally.
Active Ingredients
Ergoline dopamine agonists:
- Bromocriptine (Parlodel).
- Cabergoline (Cabaser, Dostinex)
- Dihydroergocriptine (not commercially available in many countries).
- Lisuride (out of trade in many countries).
- Pergolide (Permax, in many countries out of trade).
Non-ergoline dopamine agonists:
- Apomorphine (generic).
- Piribedil
- Pramipexole (Sifrol, generic)
- Quinagolide (Norprolac)
- Ropinirole (Requip, Adatrel, generic).
- Rotigotine (Neupro TTS)
Contraindications
Full precautions can be found in the drug label.
Interactions
Some dopamine agonists are substrates of CYP isozymes. Dopamine antagonists such as the neuroleptics may reverse the effects of dopamine agonists. Ergoline agents should not be combined with ergot alkaloids. Centrally depressant drugs and alcohol may potentiate sedative effects.
Adverse Effects
The most common possible adverse effects include (selection):
- Central nervous disorders: Dizziness, headache, drowsiness, fatigue, sleep disturbances, movement disorders (dyskinesias).
- Eye disorders: Visual disturbances
- Cardiovascular: Low blood pressure
- Gastrointestinal disorders: Dry mouth, nausea, vomiting, weight loss, constipation.
Drowsiness and sudden falling asleep are often observed and can lead to accidents. Driving and operating machinery should therefore be avoided. Dopamine agonists can also commonly cause psychiatric disorders such as unusual dreams, hallucinations, confusion, perceptual disturbances, hallucinations, depression, behavioral problems, compulsive behavior, gambling addiction, compulsive buying, binge eating, hypersexuality, and mania. This is due to the fact that dopamine is a neurotransmitter that performs many important functions in the brain, for example, related to emotions, motivation, pleasure, rewards and eating.
